Conventionally, in a printer, in order to eliminate the waste of outputting a blank in the case of a page on which image to be printed does not exist, a so-called blank page save function is known that does not output a page where an image to be printed does not exist (for example, Japanese Patent Publication No. 5-19472).
According to the foregoing method, because blank page determination is carried out in page units, during double sided printing output is not carried out when there is a page that is blank and thus the pages get out of order. As a result, the even-numbered pages, which should be printed on the back, are printed on the front, and the odd-numbered pages, which should be printed on the front, are printed on the back, leading to a result not intended by the user. For example, as shown in FIG. 15A, when one wishes to double truck the fourth page and the fifth page, and the second page (or the third page) is not output because it is blank, then, as shown in FIG. 15B, the pages get out of order, and consequently the fifth page and the sixth page are double trucked.